June 25, 2007

Historians often assume that they need pay no attention to human evolution because the process ground to a halt in the distant past. That assumption is looking less and less secure in light of new findings based on decoding human DNA.

People have continued to evolve since leaving the ancestral homeland in northeastern Africa some 50,000 years ago, both through the random process known as genetic drift and through natural selection. The genome bears many fingerprints in places where natural selection has recently remolded the human clay, researchers have found, as people in the various continents adapted to new diseases, climates, diets and, perhaps, behavioral demands.

A striking feature of many of these changes is that they are local. The genes under selective pressure found in one continent-based population or race are mostly different from those that occur in the others. These genes so far make up a small fraction of all human genes. ...

Even more strikingly, Dr. Williamson’s group reported that a version of a gene called DAB1 had become universal in Chinese but not in other populations. DAB1 is involved in organizing the layers of cells in the cerebral cortex, the site of higher cognitive functions.

Variants of two genes involved in hearing have become universal, one in Chinese, the other in Europeans.

The emerging lists of selected human genes may open new insights into the interactions between history and genetics. “If we ask what are the most important evolutionary events of the last 5,000 years, they are cultural, like the spread of agriculture, or extinctions of populations through war or disease,” said Marcus Feldman, a population geneticist at Stanford. These cultural events are likely to have left deep marks in the human genome.

A genomic survey of world populations by Dr. Feldman, Noah Rosenberg and colleagues in 2002 showed that people clustered genetically on the basis of small differences in DNA into five groups that correspond to the five continent-based populations: Africans, Australian aborigines, East Asians, American Indians and Caucasians, a group that includes Europeans, Middle Easterners and people of the Indian subcontinent. The clusterings reflect “serial founder effects,” Dr. Feldman said, meaning that as people migrated around the world, each new population carried away just part of the genetic variation in the one it was derived from.

The new scans for selection show so far that the populations on each continent have evolved independently in some ways as they responded to local climates, diseases and, perhaps, behavioral situations.

The concept of race as having a biological basis is controversial, and most geneticists are reluctant to describe it that way. But some say the genetic clustering into continent-based groups does correspond roughly to the popular conception of racial groups.

“There are difficulties in where you put boundaries on the globe, but we know now there are enough genetic differences between people from different parts of the world that you can classify people in groups that correspond to popular notions of race,” Dr. Pritchard said.

David Reich, a population geneticist at the HarvardMedicalSchool, said that the term “race” was scientifically inexact and that he preferred “ancestry.” Genetic tests of ancestry are now so precise, he said, that they can identify not just Europeans but can distinguish between northern and southern Europeans. Ancestry tests are used in trying to identify genes for disease risk by comparing patients with healthy people. People of different races are excluded in such studies. Their genetic differences would obscure the genetic difference between patients and unaffected people. [More]

For almost a decade, I've been pointing out that we know with tautological certainty that extended families exist, extended families of whatever size you wish from the tiny to the vast. And we know with as close to absolute certainty as anything can be in the human empirical world that some big extended families have a certain degree of coherence and endurance because their ancestors were not randomly outbreeding but tended to inbreed so some degree -- if you go back 1,000 years, there are 1 trillion openings in your family tree but there weren't 1 trillion people alive. So a lot of your ancestors did double duty, to say the least. So, nobody is randomly descended from the entire human race. Even if you are Tiger Woods' daughter, you can still divvy up your ancestry into Thai, Swedish, etc.

Now, what you want to call these partly inbred extended families is a subjective semantic issue. "Racial groups" strikes me as the most obvious, but if Dr. Reich wants to call them "ancestral groups," well, swell, that's a useful term too.

The point is that partly inbred extended families exist and they are important.

Has there ever been any estimate on the length of time it would have taken for speciation to occur between the various population groups?

Obviously, 50,000 years or so was not enough.

Speciation? You mean the development of different races? 50,000 years or so was apparently enough--unless there was indeed some input from archaic human beings like Neanderthals. I wouldn't underestimate the amount of change that can occur after a few hundred centuries in very small inbred groups having significant mortality rates due to environmental pressures.

Have wolves, coyotes, and dogs speciated yet? They are still interfertile, so by Ernst Mayr's defintion of species (the most popular of the 22 common definitions), they aren't separate species.

My vague impression is that there's not much point to speciation among the more flexible, intelligent sort of animals. It is really only among the dumber sort of animals where behavior is hard-coded into the genes that non-interfertility makes sense. If you are a tropical beetle that is hard-coded to live on the vertical, but not horizontal, surfaces of a mahogany tree, but not any other kind of tree, well, it makes sense to be only able to mate with other beetles with the same coding.

But if you are a smart canine that can figure out how to live in a forest, a desert, a slum, or a mansion, why bother restricting who you can mate with?

Humans, of course, make canines look like dung beetles for flexibility.

Speciation among primates - current estimate for chimp-human split is 5 million years, we're separate species (not interfertile) so it must have taken less than 5 million years. I suspect it takes around 2 million years, depending on generation length.

That would indicate that modern humans were interfertile with homo erectus and homo neanderthalis.

Modern humans are obviously not speciated. According to the standard biologists' definition of a sub-species/race, that it's merely an in-breeding group visually distinct from other sub-species/races, we are obviously sub-speciated, as any geographically dispersed species will tend to be. -ViL

"Ancestral groups" seems fine to me as the definition is right there: it's about kinship, i.e., ancestors. It's also useful to be able to differentiate between "ancestral groups" and "genetic clusters."

(BTW, and slightly off topic:I once read a thought experiment about how two identical groups were placed on two uninhabited islands in different climate zones. After 10,000 years their descendants would differ greatly from one another. This was presented as an argument against (!) the existence of races. The logic behind that conclusion wasn't presented, but I suppose some people think races must be immutable to exist.)

They are still interfertile, so by Ernst Mayr's defintion of species (the most popular of the 22 common definitions), they aren't separate species.

This is not Mayr's definition. Mayr's definition is essentially a behavioral one - do genetically separated populations breed when they occupy overlapping territories. Dawkins covers this too in Ancestor's Tale. Your understanding is also inconsistent with how important and common genetic introgression is among species... as Dr. Cochran and others have shown, especially with human beings!

Of course by this definition some could argue human races are species. For instance there are more introgressed hominoid species alleles in the human genome than there are introgressed African-American genes in the white American gene pool! Were humans and their primate cousins more likely to get it on, than whites and blacks?! Nahhhh... this is certainly a result of the exceedingly smaller time span, and by and large there are no reliable or convincing "isolating mechanisms" (behavioral or otherwise) demonstrated between any human races, who are all relatively eager to breed in overlapping territories. For example, the eventual pairing of black women and Asian men in Jamaica. (NB - Darwin spends some time in Descent of Man sincerely debating whether human races should count as species. He goes with 'no'!)

People think that some magic genetic difference number, or infertility of offspring, or inability to make offspring, or an arbitrary separation time define species, but these aren't the usual, Mayr influenced, criteria used by most biologists.

That would indicate that modern humans were interfertile with homo erectus and homo neanderthalis.

That argument still has yet to be settled. What we're fairly certain we know is that Neanderthal Man left none of his Y chromosomes in the modern gene pool. Whether they left any of their other DNA in that pool is still open to debate.

Given the animals that some modern men will try breeding with, there is no doubt that at some point, H. sapiens at least tried to breed with H. erectus. The time separation there was around 1.8 millions years.

My vague impression is that there's not much point to speciation among the more flexible, intelligent sort of animals.

That makes sense in one, uh, sense. Speciation would limit the amount of genetic diversity the new species would have at its disposal, reducing the probability of long-term survival. Retaining access to the larger gene pool would be an advantage.

But I always thought speciation indicated some genetic mechanism by which a) two separate species couldn't produce offspring together, or b) produced offspring that were infertile (like mules, zorses, etc.) If a homind group were to add a new chromosome, that would qualify it for a new species, whether it wanted to be one or not.

Was H. floresiensis (the Flores islands "hobbit people") considered speciated, or would they they still have been able to breed with the larger H. erectus population of SE Asia?

Now, what you want to call these partly inbred extended families is a subjective semantic issue. "Racial groups" strikes me as the most obvious, but if Dr. Reich wants to call them "ancestral groups," well, swell, that's a useful term too.

This is like the Great African Name-Game, if played for somewhat opposite reasons; blacks get a new name every so often because they inevitably wear out the one they have; race gets a new name every so often because the Great and the Good hate it and want to keep the rubes confused.

Has there ever been any estimate on the length of time it would have taken for speciation to occur between the various population groups?

Obviously, 50,000 years or so was not enough.

LOL! What a silly question and comment! R-A-C-E is speciation in progress. Half-baked as it was/is, it still managed to stall itself (i.e., one emergent species managed to threaten its own speciation by introducing globalization)

But if you are a smart canine that can figure out how to live in a forest, a desert, a slum, or a mansion, why bother restricting who you can mate with?

A big reason there is so much biodiversity in the tropical rain forests, according to Edward O. Wilson, is because the temperature environment is so stable. It's always warm. So, beetles, to take a famous example, speciate like crazy for every microenvironment. There's a beetle that's specialized for living on the trunks of one kind of tree and another that's specialized for living on the branches of the same tree, and so on and so forth. To borrow computer terms, the programming of how to deal with environment gets hard-coded into the genes. If the trunk beetle mates with the branch beetle, the offspring are apt to be confused.

In contrast, temperate-zone speices have to deal with major changes in the temperature environment over the course of the year. So, there is less point speciating in order to specialize in a microenvironment because the environment will change so much during the course of the year. So, you might as well soft-code your programming with lots of ability to learn to deal with different environments, since you are going to have to deal with different environments anyway over the course of the year.

LOL! What a silly question and comment! R-A-C-E is speciation in progress.

Well, obviously. But it is not speciation completed. How long would that take for a species like H. sapiens? I suspect the size of the breeding population matters - a smaller breeding population would allow genetic changes to accumulate faster, which is why Darwin found so many new species in the Galapagos.

Maybe a small hillbilly family that breeds only amongst itself?

A globally mobile population of 6.5 billion may have ended that possibility forever. But it's fascinating to think that if Columbus et al had had never happened there would eventually have been, from the South Pacific to Iceland to Madagascar, a dozen or more separate species all descended from H. sapiens.

Isn't it nice to know that every so often liberals will decide that a previously banned subject is suddenly acceptable to discuss again? Like the ban on discussing race and racial differences, which is slowly yielding to evidence from everywhere. 50 years ago people knew instinctively that there was such a thing as race. Maybe they didn't have all the magnificent data we have at our disposal now, but still people knew.

A few weeks ago NPR had an interview with Conn Iggulden, the author of the chart-topping "The Dangerous Book for Boys." When asked why it was for boys, Iggulden said: "Well, because we know boys and girls are different. 15 years ago that would have been controversial to say, but today everyone knows it's true."

15 years ago it was controversial to say it around Radio Managua listeners - in fact, it was controversial to say because of Radio Managua listeners. Now they can't hold the facts back, though.

The human tragedy: the amount of time and energy spent on denying reality is so enormous as to be virtually incomputable. It is a culture-wide plague nowadays righteously to define "thinking" as being identical to "denying plain facts."

You unthinkingly call him a crook, but he is REALLY a creative financier, crafting a new paradign.

You unthinkingly consider her a slut, but she is REALLY a liberated pan-sexual progressive, crafting a new paradign.

To the unthinking, it looks like mass murder. But it's REALLY the liberation of oppressed peoples from an old paradign.

Your job and your future have collapsed, but if you could think correctly, then you would see that "the world is flat" and this is a good thing.

It's not a bunch of you-know-whats, violent, vile, and dangerous. It's a vibrant community of differing culture, in a new paradign. Only when you deny your lying' eyes are you thinking.

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You can put money into your Google Wallet Balance from your bank account and send it with no service fee.

Google Wallet works from both a website and a smartphone app (Android and iPhone -- the Google Wallet app is currently available only in the U.S., but the Google Wallet website can be used in 160 countries).

Or, once you sign up with Google Wallet, you can simply send money via credit card, bank transfer, or Wallet Balance as an attachment from Google's free Gmail email service. Here'show to do it.

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